Naturally occurring and bioengineered apoA-I mutations that inhibit the conversion of discoidal to spherical HDL: the abnormal HDL phenotypes can be corrected by treatment with LCAT

Abstract

In the present study we have used adenovirus-mediated gene transfer of apoA-I (apolipoprotein A-I) mutants in apoA-I-/- mice to investigate how structural mutations in apoA-I affect the biogenesis and the plasma levels of HDL (high-density lipoprotein). The natural mutants apoA-I(R151C)Paris, apoA-I(R160L)Oslo and the bioengineered mutant apoA-I(R149A) were secreted efficiently from cells in culture. Their capacity to activate LCAT (lecithin:cholesterol acyltransferase) in vitro was greatly reduced, and their ability to promote ABCA1 (ATP-binding cassette transporter A1)-mediated cholesterol efflux was similar to that of WT (wild-type) apoA-I. Gene transfer of the three mutants in apoA-I-/- mice generated aberrant HDL phenotypes. The total plasma cholesterol of mice expressing the apoA-I(R160L)Oslo, apoA-I(R149A) and apoA-I(R151C)Paris mutants was reduced by 78, 59 and 61% and the apoA-I levels were reduced by 68, 64 and 55% respectively, as compared with mice expressing the WT apoA-I. The CE (cholesteryl ester)/TC (total cholesterol) ratio of HDL was decreased and the apoA-I was distributed in the HDL3 region. apoA-I(R160L)Oslo and apoA-I(R149A) promoted the formation of prebeta1 and alpha4-HDL subpopulations and gave a mixture of discoidal and spherical particles. apoA-I(R151C)Paris generated subpopulations of different sizes that migrate between prebeta and alpha-HDL and formed mostly spherical and a few discoidal particles. Simultaneous treatment of mice with adenovirus expressing any of the three mutants and human LCAT normalized plasma apoA-I, HDL cholesterol levels and the CE/TC ratio. It also led to the formation of spherical HDL particles consisting mostly of alpha-HDL subpopulations of larger size. The correction of the aberrant HDL phenotypes by treatment with LCAT suggests a potential therapeutic intervention for HDL abnormalities that result from specific mutations in apoA-I.

Apolipoprotein A-I Exerts Bactericidal Activity against Yersinia enterocolitica Serotype O:3

“…Adenoviruses expressing ⌬185-243 and ⌬220 -243 were generated as described previously (23,24). The adenoviruses expressing L218A/L219A/V221A/L222A and E223A/K226A were generated in a similar way (25).…”

Significance of the hydrophobic residues 225–230 of apoA-I for the biogenesis of HDL

“…Potential abnormalities in the HDL phenotype in apoA-I Ϫ / Ϫ mice resulting from the expression of the apoA-I[225-230] mutant were verifi ed by two-dimensional gel electrophoresis of plasma that showed the formation of pre-␤ -and ␣ 4-HDL particles. Accumulation of such particles is indicative of defective maturation of HDL due to insuffi ciency of mouse LCAT ( 11,18 ). The LCAT insufficiency may originate from fast catabolism of the nascent HDL particles along with the endogenous LCAT bound to them ( 11 ).…”

“…The LCAT insufficiency may originate from fast catabolism of the nascent HDL particles along with the endogenous LCAT bound to them ( 11 ). Fast catabolism of the nascent HDL particles by the kidney has been described previously ( 18,20 ).…”

“…In previous studies, we have shown that naturally occurring or bioengineered point mutations in apoA-I when expressed in mouse models activate LCAT insuffi ciently and in some instances may lead to the accumulation of discoidal HDL particles in plasma ( 18,19 ). Other mutations lead to very low levels of HDL cholesterol and accumulation presence of apoB-48 in the higher density fractions affected the particle composition of the HDL fraction by enriching it with larger particles corresponding in size to VLDL, IDL, and LDL.…”

“…These phenotypes were characterized by low HDL levels, preponderance of immature HDL subpopulations, or accumulation of discoidal HDL particles in plasma ( 1,10,11,15,18,19 ).…”